In certain electronic devices, such as portable electronic devices, e.g. cell phones, low-power operational amplifiers which can drive low impedance loads are used. For low power consumption and high driving capability, AB class amplifiers are a typical choice for such amplifiers. For an AB class amplifier, bias current control is needed. AB class amplifiers with bias current control that is stable, e.g. in case of varying supply voltage or varying loads, are desirable.